A turbomachine, for example a gas turbine, has a rotor which is supported at its longitudinal ends by a bearing in each case. The bearings are of the lubricated rolling bearing type or lubricated tilting pad bearing type, for example. During operation of the gas turbine, the rotor rotates at an operating speed, wherein during starting of the gas turbine the rotor is brought to the operating speed from the stationary state.
The rotor has a rotor-dynamic characteristic which especially depends both on the bearing span and on the mass inertia moment and the flexural strength of the rotor and also upon the rigidity and the damping of the bearings. The rotor-dynamic characteristic of the rotor is determined by critical speeds and the associated vibration modes of the rotor. Some critical speeds lie below the operating speed so that when running up the gas turbine the rotor must pass through these critical speeds. When passing through one of the critical speeds, the vibration amplitudes of the rotor as a rule are at their greatest, but must not exceed a maximum permissible amount. For monitoring the vibration amplitudes of the rotor, the vibration behavior of the bearings is customarily monitored. For this purpose, a vibration measuring device is customarily used for measuring the vibration of the bearing. The vibration measuring device has at least one vibration sensor which is attached to the housing of the bearing.
Measuring devices for vibration measuring are already known from documents U.S. Pat. No. 5,520,061 A, EP 2 034 275 A1, U.S. Pat. No. 4,907,456 A, and JP 60-190605 A.